Nanolasers based on a semiconductor have rotationally evolved from a vertical cavity surface emitting laser of one-dimensional photonic crystal representing a first generation nanolaser, via a two-dimensional photonic crystal laser of a second generation, to a nano-ladder laser of a third generation, which looks like a one-dimensional nanolaser.
In detail, in 1989, Bell Laboratories in U.S. has successfully made a vertical cavity surface emitting laser (VCSEL), which is a novel semiconductor laser, namely a first generation nanolaser, through experiments. The VCSEL having lengths of several microns in three directions is widely used in the industries as a short-distance optic interconnecting element in these days, and also accepted as a representative semiconductor microstructure of a resonator quantum dynamics. For this reason, the VCSEL is being actively studied in the present.
In addition, in 1999, the research team of Pref. Scherer in California Institute of Technology has observed laser oscillation from an InP thin-film two-dimensional photonic crystal resonator, which is a compound semiconductor, for the first time and made a two generation nanolaser. This may relatively easily realize great Q/V (a value obtained by dividing a quality factor by a mode volume V) by using a semiconductor-based photonic crystal resonator.
In addition, in 2008 and 2009, a nano-ladder resonator having a smaller volume in a resonance mode and a very large Q value has been proposed and implemented, thereby making a three generation nanolaser.
Among them, the VCSEL is industrially widely used for light source for short-distance optical communication, laser mouse for PC, or the like.
In order to make the two-dimensional photonic crystal resonator as an ‘available’ single photon generator which may be applied to quantum information communications, many problems should be solved in the future. In other words, it is difficult to position an optimum quantum dot at an optimum place.
The works for efficiently collecting light emitted from a very small laser and sending the light to an optical fiber or an optical detector are very important and should be studied thoroughly.